11 month old constantly sick

My 11 month old is sick all the time. He’s probably been sick 5x now since birth, has needed antibiotics twice and one shot of steroids for breathing issues. He’s constantly congested and seems to have a low grade fever every week! The doctor is not concerned and brushes it off as allergies. What’s going on!? Has anyone else had a baby that was sick this often? I hope this doesn’t continue through childhood!